Mask blank, phase shift mask, and method for manufacturing semiconductor device

ABSTRACT

A mask blank in which a phase shift film provided on a light-permeable substrate includes at least a nitrogen-containing layer and an oxygen-containing layer, the nitrogen-containing layer is made from a silicon nitride-based material and the oxygen-containing layer is made from a silicon oxide-based material, wherein, when the nitrogen-containing layer is subjected to X-ray photoelectron spectroscopy to obtain a maximum peak PSi_f of photoelectron intensity of a Si2p narrow spectrum and the light-permeable substrate is subjected to X-ray photoelectron spectroscopy to obtain a maximum peak PSi_s of photoelectron intensity of a Si2p narrow spectrum, the numerical value (PSi_f)/(PSi_s), which is produced by dividing the maximum peak PSi_f in the nitrogen-containing layer by the maximum peak PSi_s in the light-permeable substrate, is 1.09 or less.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/970,601, filed Jan. 8, 2019, which is a National Stage ofInternational Application No. PCT/JP2019/000138, filed Jan. 8, 2019,which claims priority to Japanese Patent Application No. 2018-029428,filed Feb. 22, 2018, and the entire contents of which is incorporated byreference in its entirety.

TECHNICAL FIELD

This disclosure relates to a mask blank and a phase shift maskmanufactured using the mask blank. This disclosure also relates to amethod for manufacturing a semiconductor device using theabove-mentioned phase shift mask.

BACKGROUND ART

In a manufacturing process of a semiconductor device, formation of afine pattern is carried out using photolithography. For the formation ofthe fine pattern, a number of transfer masks are normally used. In orderto miniaturize a pattern of the semiconductor device, it is necessary toshorten a wavelength of an exposure light source used in thephotolithography in addition to miniaturization of mask patterns formedon the transfer masks. In recent years, an ArF excimer laser (wavelengthof 193 nm) is increasingly used as the exposure light source uponmanufacturing the semiconductor device.

As one type of the transfer masks, a halftone phase shift mask is known.The halftone phase shift mask has a light-transmitting portion allowingexposure light to be transmitted therethrough and a phase shift portion(of a halftone phase shift film) allowing the exposure light to betransmitted therethrough in an attenuated state, and substantiallyreverses (with a phase difference of about 180 degrees) a phase of theexposure light transmitted through the phase shift portion with respectto a phase of the exposure light transmitted through thelight-transmitting portion. Due to the phase difference, a contrast ofan optical image at a boundary between the light-transmitting portionand the phase shift portion is enhanced so that the halftone phase shiftmask becomes a high-resolution transfer mask.

The halftone phase shift mask has a tendency that a transferred imagehas a higher contrast as the halftone phase shift film has a highertransmittance with respect to the exposure light. Therefore, mainly incase where an especially high resolution is required, a so-calledhigh-transmittance halftone phase shift mask is used. For the phaseshift film of the halftone phase shift mask, a molybdenum silicide(MoSi) based material is widely used. However, it has recently beenfound out that an MoSi-based film is low in resistance against exposurelight of the ArF excimer laser (so-called ArF lightfastness).

As the phase shift film of the halftone phase shift mask, an SiN-basedmaterial comprising silicon and nitrogen is also known and is disclosedin, for example, Patent Document 1. Furthermore, as a technique forobtaining desired optical characteristics, Patent Document 2 discloses ahalftone phase shift mask using a phase shift film comprising a periodicmultilayer film including Si oxide layers and Si nitride layers. PatentDocument 2 describes that a predetermined phase difference is obtainedat a transmittance of 5% with respect to light having a wavelength of157 nm, i.e., F₂ excimer laser light. Since the SiN-based material hashigh ArF lightfastness, attention is focused on a high-transmittancehalftone phase shift mask using the SiN-based film as the phase shiftfilm.

PRIOR ART DOCUMENT(S) Patent Document(s)

Patent Document 1: JP H7-134392 A

Patent Document 2: JP 2002-535702 A

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

In case where a single-layer phase shift film of a silicon nitridematerial is used, restriction is imposed on a transmittance with respectto exposure light of the ArF excimer laser (hereinafter referred to asArF exposure light). It is therefore difficult to increase thetransmittance to more than 18% in view of optical characteristics of thematerial.

By introducing oxygen into silicon nitride, the transmittance can beincreased. However, if a single-layer phase shift film of a siliconoxynitride material is used, there is a problem that, when the phaseshift film is patterned by dry etching, etching selectivity is reducedwith respect to a transparent substrate formed of a material containingsilicon oxide as a main component.

As a method of resolving the above-mentioned problem, for example, amethod of forming a phase shift film into a two-layer structurecomprising a silicon nitride layer and a silicon oxide layer arranged inthis order from the transparent substrate is conceivable. PatentDocument 1 discloses the halftone phase shift mask having the phaseshift film of the two-layer structure comprising the silicon nitridelayer and the silicon oxide layer arranged in this order from thetransparent substrate.

By forming the phase shift film into the two-layer structure comprisingthe silicon nitride layer and the silicon oxide layer, a degree offreedom in refractive index with respect to the ArF exposure light,extinction coefficient and film thickness is increased so that the phaseshift film of the two-layer structure has a desired transmittance and adesired phase difference with respect to the ArF exposure light.However, as a result of thorough study, it has been found out that thehalftone phase shift mask having the phase shift film of the two-layerstructure comprising the silicon nitride layer and the silicon oxidelayer has problems which will hereinafter be described.

As compared with the above-mentioned MoSi-based film, both of thesilicon nitride layer and the silicon oxide layer are considerably highin ArF lightfastness. However, the silicon nitride layer is low in ArFlightfastness as compared with the silicon oxide layer. Thus, in casewhere the phase shift mask is manufactured using a mask blank having thephase shift film mentioned above and the phase shift mask is set in anexposure apparatus and repeatedly subjected to exposure transfer by theArF exposure light, a line width of a pattern of the phase shift filmtends to be thickened at a part in the silicon nitride layer as comparedwith a part in the silicon oxide layer. Accordingly, there is a problemthat, although the part in the silicon oxide layer is hardly thickenedagainst repeated irradiation with the ArF exposure light, thickening ofthe line width of the pattern in the entire phase shift film becomesrelatively large when the phase shift film is subjected to the repeatedirradiation with the ArF exposure light.

Both of the silicon nitride layer and the silicon oxide layer areconsiderably high in resistance (chemical resistance) against a chemicalsolution used in cleaning or the like, as compared with theabove-mentioned MoSi-based film. However, the silicon nitride layer islow in chemical resistance as compared with the silicon oxide layer.Thus, in case where cleaning with the chemical solution is repeatedlycarried out in the middle of manufacturing the phase shift mask from themask blank having the above-mentioned phase shift film or after thephase shift mask is manufactured, the line width of the pattern of thephase shift film could easily be reduced at the part in the siliconnitride layer as compared with the part in the silicon oxide layer.Accordingly, there is a problem that, although the silicon oxide layeris high in chemical resistance, the amount of reduction in line width ofthe pattern in the entire phase shift film becomes relatively large whencleaning with the chemical solution is repeatedly carried out.

On the other hand, in case where the above-mentioned phase shift filmhaving the two-layer structure has a configuration in which a materialforming a high-transmission layer is changed from silicon oxide intosilicon oxynitride, it is possible to obtain optical characteristicssimilar to those in case where the high-transmission layer is formed ofsilicon oxide. However, even in case of the phase shift film having theabove-mentioned configuration, there arise the problems of the ArFlightfastness and the chemical resistance.

This disclosure has been made in order to solve the above-mentionedproblems. It is an aspect of this disclosure to provide a mask blankwhich has a phase shift film formed on a transparent substrate and atleast containing a nitrogen-containing layer, such as a silicon nitridelayer, and an oxygen-containing layer, such as a silicon oxide layer,and which is for use in a halftone phase shift mask and is improved inArF lightfastness and chemical resistance in the entire phase shiftfilm.

In addition, it is an aspect of this disclosure to provide a phase shiftmask manufactured using the above-mentioned mask blank.

Furthermore, it is an aspect of this disclosure to provide a method formanufacturing the above-mentioned phase shift mask.

Moreover, it is an aspect of this disclosure to provide a method formanufacturing a semiconductor device using the above-mentioned phaseshift mask.

Means to Solve the Problem

In order to solve the above-mentioned problems, this disclosure has thefollowing configurations.

(Configuration 1)

A mask blank comprising a transparent substrate and a phase shift filmformed thereon,

wherein the phase shift film at least contains a nitrogen-containinglayer and an oxygen-containing layer;

wherein the oxygen-containing layer is formed of a material consistingof silicon and oxygen or a material consisting of oxygen, silicon, andone or more elements selected from metalloid elements and non-metalelements;

wherein the nitrogen-containing layer is formed of a material consistingof silicon and nitrogen or a material consisting of nitrogen, silicon,and one or more elements selected from non-metal elements and metalloidelements; and

wherein, when the nitrogen-containing layer is subjected to X-rayphotoelectron spectroscopy to obtain a maximum peak PSi_f ofphotoelectron intensity of an Si2p narrow spectrum in thenitrogen-containing layer and the transparent substrate is subjected tothe X-ray photoelectron spectroscopy to obtain a maximum peak PSi_s ofphotoelectron intensity of an Si2p narrow spectrum in the transparentsubstrate, a numerical value (PSi_f)/(PSi_s) is 1.09 or less where thenumerical value is obtained by dividing the maximum peak PSi_f in thenitrogen-containing layer by the maximum peak PSi_s in the transparentsubstrate.

(Configuration 2)

The mask blank according to Configuration 1, wherein thenitrogen-containing layer has a nitrogen content of 50 atomic % or more.

(Configuration 3)

The mask blank according to Configuration 1 or 2, wherein theoxygen-containing layer has a total content of nitrogen and oxygen of 50atomic % or more.

(Configuration 4)

The mask blank according to any one of Configurations 1 to 3, whereinthe oxygen-containing layer has an oxygen content of 15 atomic % ormore.

(Configuration 5)

The mask blank according to any one of Configurations 1 to 4, whereinthe maximum peak of photoelectron intensity in the Si2p narrow spectrumis the maximum peak at a bond energy within a range of 96 [eV] or moreand 106 [eV] or less.

(Configuration 6)

The mask blank according to any one of Configurations 1 to 5, whereinX-rays emitted to the phase shift film in the X-ray photoelectronspectroscopy are AlKα rays.

(Configuration 7)

The mask blank according to any one of Configurations 1 to 6, wherein aratio obtained by dividing the number of existing Si₃N₄ bonds in thenitrogen-containing layer by a total number of the existing Si₃N₄ bonds,existing Si_(a)N_(b) bonds (where b/[a+b]<4/7), existing Si—Si bonds,existing Si—O bonds, and existing Si—ON bonds is 0.88 or more.

(Configuration 8)

The mask blank according to any one of Configurations 1 to 7, whereinthe phase shift film has a function of allowing exposure light of an ArFexcimer laser to be transmitted therethrough at a transmittance of 10%or more and a function of causing a phase difference of 150 degrees ormore and 200 degrees or less between the exposure light transmittedthrough the phase shift film and the exposure light transmitted throughair for a same distance as a thickness of the phase shift film.

(Configuration 9)

The mask blank according to any one of Configurations 1 to 8, comprisinga light shielding film formed on the phase shift film.

(Configuration 10)

A phase shift mask comprising a transparent substrate and a phase shiftfilm with a transfer pattern formed thereon,

wherein the phase shift film at least includes a nitrogen-containinglayer and an oxygen-containing layer;

wherein the oxygen-containing layer is formed of a material consistingof silicon and oxygen or a material consisting of oxygen, silicon, andone or more elements selected from metalloid elements and non-metalelements;

wherein the nitrogen-containing layer is formed of a material consistingof silicon and nitrogen or a material consisting of nitrogen, silicon,and one or more elements selected from non-metal elements and metalloidelements; and

wherein, when the nitrogen-containing layer is subjected to X-rayphotoelectron spectroscopy to obtain a maximum peak PSi_f ofphotoelectron intensity of an Si2p narrow spectrum in thenitrogen-containing layer and the transparent substrate is subjected tothe X-ray photoelectron spectroscopy to obtain a maximum peak PSi_s ofphotoelectron intensity of an Si2p narrow spectrum in the transparentsubstrate, a numerical value (PSi_f)/(PSi_s) is 1.09 or less where thenumerical value is obtained by dividing the maximum peak PSi_f in thenitrogen-containing layer by the maximum peak PSi_s in the transparentsubstrate

(Configuration 11)

The phase shift mask according to Configuration 10, wherein thenitrogen-containing layer has a nitrogen content of 50 atomic % or more.

(Configuration 12)

The phase shift mask according to Configuration 10 or 11, wherein theoxygen-containing layer has a total content of nitrogen and oxygen of 50atomic % or more.

(Configuration 13)

The phase shift mask according to any one of Configurations 10 to 12,wherein the oxygen-containing layer has an oxygen content of 15 atomic %or more.

(Configuration 14)

The phase shift mask according to any one of Configurations 10 to 13,wherein the maximum peak of photoelectron intensity in the Si2p narrowspectrum is the maximum peak at a bond energy within a range of 96 [eV]or more and 106 [eV] or less.

(Configuration 15)

The phase shift mask according to any one of Configurations 10 to 14,wherein X-rays emitted to the phase shift film in the X-rayphotoelectron spectroscopy are AlKα rays.

(Configuration 16)

The phase shift mask according to any one of Configurations 10 to 15,wherein a ratio obtained by dividing the number of existing Si₃N₄ bondsin the nitrogen-containing layer by a total number of the existing Si₃N₄bonds, existing Si_(a)N_(b) bonds (where b/[a+b]<4/7), existing Si—Sibonds, existing Si—O bonds, and existing Si—ON bonds is 0.88 or more.

(Configuration 17)

The phase shift mask according to any one of Configurations 10 to 16,wherein the phase shift film has a function of allowing exposure lightof an ArF excimer laser to be transmitted therethrough at atransmittance of 10% or more and a function of causing a phasedifference of 150 degrees or more and 200 degrees or less between theexposure light transmitted through the phase shift film and the exposurelight transmitted through air for a same distance as a thickness of thephase shift film.

(Configuration 18)

The phase shift mask according to any one of Configurations 10 to 17,comprising a light shielding film formed on the phase shift film andprovided with a light shielding pattern.

(Configuration 19)

A method of manufacturing a semiconductor device, comprising the step ofexposure-transferring a transfer pattern onto a resist film on asemiconductor substrate, using the phase shift mask according to any oneof Configurations 10 to 18.

Effect of the Invention

A mask blank according to this disclosure, comprising a transparentsubstrate and a phase shift film formed thereon, wherein the phase shiftfilm at least contains a nitrogen-containing layer and anoxygen-containing layer; wherein the oxygen-containing layer is formedof a material consisting of silicon and oxygen or a material consistingof oxygen, silicon, and one or more elements selected from metalloidelements and non-metal elements; wherein the nitrogen-containing layeris formed of a material consisting of silicon and nitrogen or a materialconsisting of nitrogen, silicon, and one or more elements selected fromnon-metal elements and metalloid elements; and wherein, when thenitrogen-containing layer is subjected to X-ray photoelectronspectroscopy to obtain a maximum peak PSi_f of photoelectron intensityof an Si2p narrow spectrum in the nitrogen-containing layer and thetransparent substrate is subjected to the X-ray photoelectronspectroscopy to obtain a maximum peak PSi_s of photoelectron intensityof an Si2p narrow spectrum in the transparent substrate, a numericalvalue (PSi_f)/(PSi_s) is 1.09 or less where the numerical value isobtained by dividing the maximum peak PSi_f in the nitrogen-containinglayer by the maximum peak PSi_s in the transparent substrate. By formingthe mask blank into the above-mentioned structure, it is possible toimprove ArF lightfastness and chemical resistance in the entire phaseshift film.

A phase shift mask according to this disclosure is characterized in thata phase shift film having a transfer pattern is similar in structure tothe phase shift film of the above-mentioned mask blank of thisdisclosure. By forming the phase shift mask as mentioned above, it ispossible to improve ArF lightfastness and chemical resistance in theentire phase shift film. Accordingly, the phase shift mask according tothis disclosure is high in transfer accuracy when exposure transfer iscarried out on a transfer object such as a resist film on asemiconductor substrate.

A method for manufacturing a semiconductor device according to thisdisclosure is characterized by comprising a step ofexposure-transferring a transfer pattern to a resist film on asemiconductor substrate by using the above-mentioned phase shift mask ofthis disclosure. Therefore, by the method for manufacturing thesemiconductor device according to this disclosure, it is possible tocarry out exposure transfer of the transfer pattern to the resist filmwith high transfer accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view for illustrating a configuration of a maskblank in an embodiment of this disclosure;

FIGS. 2A to 2F are sectional views for illustrating a manufacturingprocess of a phase shift mask in the embodiment of this disclosure;

FIG. 3 is a view for illustrating a result (Si2p narrow spectrum)obtained by carrying out X-ray photoelectron spectroscopy on a phaseshift film and a transparent substrate of a mask blank according toExample 1 of this disclosure; and

FIG. 4 is a view for illustrating a result (Si2p narrow spectrum)obtained by carrying out X-ray photoelectron spectroscopy on a phaseshift film and a transparent substrate of a mask blank according toComparative Example 1.

MODE FOR EMBODYING THE INVENTION

At first, a process leading to completion of this disclosure will bedescribed. With respect to a case where a phase shift film of a maskblank has a layered structure comprising a silicon nitride-basedmaterial film (nitrogen-containing layer) and a silicon oxide-basedmaterial layer (oxygen-containing layer), the present inventorsconducted a research in view of ArF lightfastness and chemicalresistance of the phase shift film.

It is supposed that a line width of a pattern of a silicon-basedmaterial layer is thickened under irradiation with ArF exposure lightbecause volume expansion occurs due to progress of a reaction in whichsilicon atoms bonded with other elements (including other silicon atoms)are excited to break those bonds and then bonded with oxygen. Therefore,in case of a silicon oxide-based material layer in which a large amountof silicon already bonded with oxygen are present at a stage beforeirradiation with the ArF exposure light, a pattern line width is hardlythickened due to the volume expansion even under the irradiation withthe ArF exposure light. Furthermore, silicon bonded with oxygen isdifficult to be dissolved in a chemical solution as compared withsilicon bonded with other elements except oxygen.

By making the silicon nitride-based material layer contain oxygen, it ispossible to improve the ArF lightfastness and the chemical resistance.However, when the silicon nitride-based material layer contains oxygen,a refractive index n and an extinction coefficient k are inevitablydecreased and the degree of freedom in designing the phase shift film issignificantly lowered. Therefore, the above-mentioned means is difficultto apply.

As a result of diligent research, the present inventors reached an ideathat the ArF lightfastness in the entire phase shift film might beimproved if, among silicon nitride-based materials, a siliconnitride-based material in which silicon is hardly excited when it isirradiated with the ArF exposure light is used as the siliconnitride-based material layer.

The present inventors conceived of an idea of using X-ray photoelectronspectroscopy (XPS) as an index indicating whether or not silicon in thesilicon nitride-based material layer is easily excited when the layer isirradiated with the ArF exposure light. At first, it has been consideredto carry out the X-ray photoelectron spectroscopy on the siliconnitride-based material layer to acquire an Si2p narrow spectrum and touse a difference in maximum peak thereof as the index. The maximum peakof photoelectron intensity of the Si2p narrow spectrum in the siliconnitride-based material layer corresponds to the number of photoelectronsemitted from nitrogen-silicon bonds per unit time. The photoelectronsare electrons which are excited in response to irradiation with X-raysand ejected from an atomic orbital. A material which is easily excitedand emits a large number of photoelectrons when it is irradiated withthe X-rays is a material having a small work function. The siliconnitride-based material having the small work function is said to be amaterial easily excited in response to the irradiation with the ArFexposure light also.

However, the number of photoelectrons detected by the X-rayphotoelectron spectroscopy varies depending on measurement conditions(the type of the X-rays to be used, irradiation intensity, and so on)even in the same silicon nitride-based material layer and, therefore,cannot directly be used as the index. As a result of research about thisproblem, the inventors reached an idea of using, as the index, anumerical value obtained by dividing the maximum peak of photoelectronintensity of the Si2p narrow spectrum in the silicon nitride-basedmaterial layer by the maximum peak of photoelectron intensity of theSi2p narrow spectrum in the transparent substrate.

The transparent substrate is formed of a relatively stable materialcontaining SiO₂ as a main component. The transparent substrate used inthe mask blank is required to be very small in variation of thematerial, for example, small in variation of optical characteristics.Therefore, variation in work function of each material is very smallamong a plurality of transparent substrates. In case of the samemeasurement conditions, a difference in maximum peak of photoelectronintensity of the Si2p narrow spectrum is small among differenttransparent substrates. Therefore, an influence of a difference inmeasurement conditions is significantly reflected on the maximum peak ofphotoelectron intensity. The maximum peak of photoelectron intensity ofthe Si2p narrow spectrum in the transparent substrate is the number ofphotoelectrons emitted from the oxygen-silicon bonds per unit time butis a suitable reference value to correct the difference in maximum peakof photoelectron intensity of the Si2p narrow spectrum in the siliconnitride-based material layer due to the difference in measurementconditions.

As a result of a further diligent research, the present inventorsreached a conclusion that, in a mask blank having a phase shift film atleast containing a silicon nitride-based material layer(nitrogen-containing layer) and a silicon oxide-based material layer(oxygen-containing layer) which are formed on a transparent substrate,ArF lightfastness can be improved if, in case where the X-rayphotoelectron spectroscopy is carried out on the silicon nitride-basedmaterial layer and the transparent substrate, a numerical value(PSi_f)/(PSi_s) is 1.09 or less where the numerical value is obtained bydividing the maximum peak PSi_f of photoelectron intensity of an Si2pnarrow spectrum in the silicon nitride-based material layer by themaximum peak PSi_s of photoelectron intensity of an Si2p narrow spectrumin the transparent substrate.

On the other hand, in the silicon nitride-based material layer with theabove-mentioned numerical value (PSi_f)/(PSi_s) of 1.09 or less, siliconin the layer is hardly excited in response to the irradiation with theArF exposure light. Such a silicon nitride-based material layer is saidto have a high abundance ratio of nitrogen-silicon bonds in a strongbonding condition. When the silicon nitride-based material layer iscontacted by a chemical solution, the nitrogen-silicon bonds aredifficult to be broken and difficult to be dissolved in the chemicalsolution.

As a result of the above-mentioned diligent research, a mask blank ofthis disclosure has been derived. Specifically, the mask blank accordingto this disclosure comprises a transparent substrate and a phase shiftfilm formed thereon. The phase shift film at least contains anitrogen-containing layer (silicon nitride-based material layer) and anoxygen-containing layer (silicon oxide-based material layer). Theoxygen-containing layer is formed of a material consisting of siliconand oxygen or a material consisting of oxygen, silicon, and one or moreelements selected from metalloid elements and non-metal elements. Thenitrogen-containing layer is formed of a material consisting of siliconand nitrogen or a material consisting of nitrogen, silicon, and one ormore elements selected from non-metal elements and metalloid elements.When the nitrogen-containing layer is subjected to the X-rayphotoelectron spectroscopy to obtain a maximum peak PSi_f ofphotoelectron intensity of an Si2p narrow spectrum in thenitrogen-containing layer and the transparent substrate is subjected tothe X-ray photoelectron spectroscopy to obtain a maximum peak PSi_s ofphotoelectron intensity of an Si2p narrow spectrum in the transparentsubstrate, a numerical value (PSi_f)/(PSi_s) is equal to 1.09 or lesswhere the numerical value is obtained by dividing the maximum peak PSi_fin the nitrogen-containing layer by the maximum peak PSi_s in thetransparent substrate.

Next, an embodiment of this disclosure will be described. A mask blankaccording to this disclosure is applicable to a mask blank for use inproducing a phase shift mask. Hereinafter, description will be made of amask blank for use in manufacturing a halftone phase shift mask.

FIG. 1 is a sectional view for illustrating a configuration of a maskblank 100 according to the embodiment of this disclosure. The mask blank100 illustrated in FIG. 1 has a structure in which a phase shift film 2,a light shielding film 3, and a hard mask film 4 are formed as layers ona transparent substrate 1 in this order.

The transparent substrate 1 may be formed of a glass material such assynthetic quartz glass, quartz glass, aluminosilicate glass, soda limeglass, and low-thermal-expansion glass (SiO₂—TiO₂ glass or the like).Among others, the synthetic quartz glass is particularly preferable as amaterial for use in forming the transparent substrate of the mask blankbecause of a high transmittance with respect to ArF excimer laser light(wavelength of 193 nm).

The phase shift film 2 is required to have a transmittance allowing aphase shift effect to effectively function. The phase shift film 2 is atleast required to have a transmittance of 1% or more with respect to ArFexposure light. The phase shift film 2 preferably has a transmittance of10% or more, more preferably 15% or more, further preferably 20% ormore, with respect to the ArF exposure light.

The phase shift film 2 is preferably adjusted to have a transmittance of40% or less, more preferably 30% or less, with respect to the ArFexposure light.

In recent years, NTD (Negative Tone Development) has become used as anexposure and development process for a resist film on a semiconductorsubstrate (wafer). In the NTD, a bright field mask (transfer mask havinga high pattern aperture) is frequently used. In a bright-field phaseshift mask, a balance between zeroth-order light and first-order lightof light transmitted through a light-transmitting portion is improved bymaking the phase shift film have a transmittance of 10% or more withrespect to exposure light. When the above-mentioned balance is improved,an effect of attenuating a light intensity due to an interference by theexposure light transmitted through the phase shift film against thezeroth-order light is further increased so that pattern resolution onthe resist film is improved. Accordingly, the transmittance of the phaseshift film 2 with respect to the ArF exposure light is preferably 10% ormore. In case where the transmittance with respect to the ArF exposurelight is 15% or more, a pattern edge enhancement effect of a transferimage (projected optical image) by a phase shift effect is furtherimproved. On the other hand, the transmittance of the phase shift film 2exceeding 40% with respect to the ArF exposure light is not preferablebecause the effect of a side lobe becomes excessively strong.

In order to obtain an appropriate phase shift effect, the phase shiftfilm 2 is required to have a function of producing a predetermined phasedifference between the ArF exposure light transmitted therethrough andlight transmitted through air for a same distance as the thickness ofthe phase shift film 2. The phase difference is preferably adjusted tofall within a range of 150 degrees or more and 200 degrees or less. Thelower limit of the phase difference in the phase shift film 2 ispreferably 160 degrees or more, more preferably 170 degrees or more. Onthe other hand, the upper limit of the phase difference in the phaseshift film 2 is more preferably 190 degrees or less.

The phase shift film 2 preferably has a thickness of 90 nm or less, morepreferably 80 nm or less. On the other hand, the phase shift film 2preferably has a thickness of 40 nm or more. If the thickness of thephase shift film 2 is smaller than 40 nm, a predetermined transmittanceand a predetermined phase difference required as the phase shift filmmight not be obtained.

The phase shift film 2 is a layered film having two or more layers atleast comprising a nitrogen-containing layer (silicon nitride-basedmaterial layer) and an oxygen-containing layer (silicon oxide-basedmaterial layer). The phase shift film 2 essentially has to comprise atleast one nitrogen-containing layer and at least one oxygen-containinglayer and may further comprise one or more nitrogen-containing layersand one or more oxygen-containing layers. For example, the phase shiftfilm 2 may have a structure comprising two or more layered structureseach of which comprises a nitrogen-containing layer and anoxygen-containing layer (layered structure of four or more layers), ormay have a structure comprising an oxygen-containing layer between twonitrogen-containing layers. The phase shift film 2 may have any materiallayer(s) other than the nitrogen-containing layer and theoxygen-containing layer as far as the effect of this disclosure isobtained.

The nitrogen-containing layer is preferably formed of a materialconsisting of silicon and nitrogen, or a material consisting ofnitrogen, silicon, and one or more elements selected from non-metalelements and metalloid elements. The nitrogen-containing layer maycontain any metalloid element(s). Among the metalloid elements, one ormore elements selected from boron, germanium, antimony, and telluriumare preferably contained because an increase in conductivity of siliconused as a sputtering target is expected.

The nitrogen-containing layer may contain any non-metal element(s). Thenon-metal elements in this case include narrow-sense non-metal elements(nitrogen, carbon, oxygen, phosphorus, sulfur, and selenium), halogens,and noble gases. Among the non-metal elements, one or more elementsselected from carbon, fluorine, and hydrogen are preferably contained.The nitrogen-containing layer preferably has an oxygen content of 10atomic % or less, more preferably 5 atomic % or less, further preferablydo not positively contain oxygen (not higher than a detection lowerlimit when composition analysis is carried out by the X-rayphotoelectron spectroscopy or the like). If the oxygen content of thenitrogen-containing layer is large, a difference in opticalcharacteristics from the oxygen-containing layer becomes small and thedegree of freedom in designing the phase shift film is reduced.

The nitrogen-containing layer may contain a noble gas. The noble gas isan element which is capable of increasing a film-forming rate andimproving productivity by presence in a film-forming chamber uponforming the nitrogen-containing layer by reactive sputtering. The noblegas is converted into plasma to collide with a target so that targetconstituent elements are ejected from the target and, while introducinga reactive gas in the middle, the nitrogen-containing layer is formed onthe transparent substrate 1. During a period after the targetconstituent elements are ejected from the target and before they areadhered to the transparent substrate 1, the noble gas in thefilm-forming chamber is slightly introduced. Preferable elements as thenoble gas required in the reactive sputtering may be argon, krypton, andxenon. In order to relax stress in the nitrogen-containing layer, heliumand neon, which are small in atomic weight, may positively beintroduced.

The nitrogen-containing layer preferably has a nitrogen content of 50atomic % or more. In a silicon-based film, a refractive index n withrespect to the ArF exposure light is very small and an extinctioncoefficient k with respect to the ArF exposure light is large.Hereinafter, the refractive index n as a simple expression refers to therefractive index n with respect to the ArF exposure light. Theextinction coefficient k as a simple expression refers to the refractiveindex k with respect to the ArF exposure light. As the nitrogen contentin the silicon-based film is increased, the refractive index n tends tobe larger and the extinction coefficient k tends to be smaller. Takinginto account that the predetermined transmittance required to the phaseshift film 2 is assured while the phase difference is assured with asmaller thickness, the nitrogen content in the nitrogen-containing layeris preferably 50 atomic % or more, more preferably 51 atomic % or more,further preferably 52 atomic % or more. The nitrogen content in thenitrogen-containing layer is preferably 57 atomic % or less, morepreferably 56 atomic % or less. If the nitrogen-containing layercontains nitrogen at a mixing ratio greater than that in Si₃N₄, it isdifficult to form the nitrogen-containing layer into an amorphous or amicrocrystalline structure. In addition, surface roughness of thenitrogen-containing layer is seriously degraded.

The nitrogen-containing layer preferably has a silicon content of 35atomic % or more, more preferably 40 atomic % or more, furtherpreferably 45 atomic % or more.

The nitrogen-containing layer is preferably formed of a materialconsisting of silicon and nitrogen. In this case, it may be recognizedthat the material consisting of silicon and nitrogen encompasses amaterial containing a noble gas.

When the nitrogen-containing layer is subjected to the X-rayphotoelectron spectroscopy to acquire the maximum peak PSi_f ofphotoelectron intensity of an Si2p narrow spectrum in thenitrogen-containing layer and the transparent substrate 1 is subjectedto the X-ray photoelectron spectroscopy to acquire the maximum peakPSi_s of photoelectron intensity of an Si2p narrow spectrum in thetransparent substrate 1, a numerical value (PSi_f)/(PSi_s) is preferably1.09 or less where the numerical value is obtained by dividing themaximum peak PSi_f in the nitrogen-containing layer by the maximum peakPSi_s in the transparent substrate 1. As described above, thenitrogen-containing layer with the numerical value (PSi_f)/(PSi_s) of1.09 or less is difficult to be excited in response to irradiation withthe ArF exposure light. By forming such nitrogen-containing layer, it ispossible to increase the ArF lightfastness. As described above, thenitrogen-containing layer has a high abundance ratio of nitrogen-siliconbonds in a strong bonding condition. By forming such nitrogen-containinglayer, it is possible to improve chemical resistance. The numericalvalue (PSi_f)/(PSi_s) is preferably 1.085 or less, more preferably 1.08or less.

On the other hand, in case of dry etching with a fluorine-based gas,such as SF₆, which is carried out in patterning the phase shift film 2,the nitrogen-containing layer is high in etching rate as compared withthe oxygen-containing layer. Therefore, when the phase shift film 2 ispatterned by dry etching, unevenness tends to easily occur on a sidewall of a pattern.

In case where the nitrogen-containing layer is patterned by the dryetching using the fluorine-based gas, fluorine atoms in an excited statebreak the nitrogen-silicon bonds to produce and volatilize siliconfluoride having a relatively low boiling point so that a pattern isformed on the nitrogen-containing layer. Since the nitrogen-siliconbonds are hardly broken in the nitrogen-containing layer having thenumerical value (PSi_f)/(PSi_s) of 1.09 or less, it is said that theetching rate of the dry etching with respect to the fluorine-based gasis reduced. Thus, a difference in etching rate between thenitrogen-containing layer and the oxygen-containing layer of the phaseshift film 2 becomes small so as to reduce the unevenness of the sidewall of the pattern formed on the phase shift film 2 by dry etching.

On the other hand, as a technique of repairing a mask defect in thehalftone phase shift mask, use may be made of a defect repairingtechnique of etching and removing a black defect portion of the phaseshift film by irradiating the black defect portion with an electron beamwhile supplying a xenon difluoride (XeF₂) gas to that portion to convertthe black defect portion into volatile fluoride. Hereinafter, suchdefect repair carried out by irradiation with charged particles such asthe electron beam will simply be called EB defect repair. In case wherethe EB defect repair is carried out on the phase shift film 2 after thetransfer pattern is formed, a repair rate of the nitrogen-containinglayer tends to be high as compared with that of the oxygen-containinglayer. In addition, in case of the EB defect repair, etching isperformed on the pattern of the phase shift film 2 in a state where theside wall is exposed. Therefore, side etching, which is etchingprogressing in a side wall direction of the pattern, easily entersparticularly into the nitrogen-containing layer. Accordingly, a patternshape after the EB defect repair tends to be an uneven shape withunevenness formed between the nitrogen-containing layer and theoxygen-containing layer.

The XeF₂ gas used in the EB defect repair is known as an etching gas inan unexcited state when the silicon-based material is subjected toisotropic etching. The above-mentioned etching is performed by a processincluding surface adsorption of the XeF₂ gas in the unexcited state tothe silicon-based material, separation into Xe and F, production ofhigh-order silicon fluoride, and volatilization. In the EB defect repairfor a thin film pattern of the silicon-based material, a black defectportion of the thin film pattern is supplied with a fluorine-based gasin the unexcited state, such as XeF₂ gas. The fluorine-based gas isadsorbed to a surface of the black defect portion and then the blackdefect portion is irradiated with the electron beam. Consequently,silicon atoms in the black defect portion are excited and forming a bondwith fluorine is promoted so that high-order silicon fluoride isproduced and volatilized at a considerably higher speed than that incase of no irradiation with the electron beam. The nitrogen-containinglayer which emits a less number of photoelectrons and is hardly excitedwhen it is irradiated with the X-rays is said to be a material which ishardly excited also in response to irradiation with the electron beam.

The nitrogen-containing layer having the above-mentioned numerical value(PSi_f)/(PSi_s) of 1.09 or less is hardly excited in response to theirradiation with the electron beam so that a repair rate can bedecreased when the EB defect repair is carried out. Thus, a differencein repair rate in the EB defect repair between the nitrogen-containinglayer and the oxygen-containing layer of the phase shift film 2 becomessmall so as to decrease the unevenness of the side wall of the patternat a position where the EB defect repair of the phase shift film 2 iscarried out.

In the X-ray photoelectron spectroscopy mentioned above, either AlKαrays or MgKα rays are applicable as the X-rays for irradiation to thetransparent substrate 1 and the nitrogen-containing layer of the phaseshift film 2 but the AlKα rays are preferably used. In the presentspecification, description is made about the case where the X-rayphotoelectron spectroscopy is carried out by using the AlKα rays as theX-rays.

A method of acquiring an Si2p narrow spectrum by carrying out the X-rayphotoelectron spectroscopy on the transparent substrate 1 and thenitrogen-containing layer is generally carried out through the followingsteps. Specifically, wide scanning for acquiring photoelectron intensity(the number of emitted photoelectrons per unit time from a measuredobject irradiated with the X-rays) in a wide bandwidth of a bond energyis at first carried out to acquire a wide spectrum and all peaks derivedfrom constituent elements of the transparent substrate 1 and thenitrogen-containing layer are identified. Thereafter, narrow scanninghigher in resolution than the wide scanning but narrower in availablebandwidth of the bond energy is carried out in a bandwidth around thepeak (Si2p) on which attention is focused. On the other hand, for thetransparent substrate 1 or the nitrogen-containing layer as the measuredobject for which the X-ray photoelectron spectroscopy is used in thisdisclosure, constituent elements are known in advance. In addition, thenarrow spectrum required in this disclosure is limited to the Si2pnarrow spectrum. Therefore, in this disclosure, the Si2p narrow spectrummay be obtained without performing the process of acquiring the widespectrum.

The maximum peak (PSi_s, PSi_f) of photoelectron intensity in the Si2pnarrow spectrum obtained by carrying out the X-ray photoelectronspectroscopy on the transparent substrate 1 or the nitrogen-containinglayer is preferably the maximum peak at the bond energy in a range of 96[eV] or more and 106 [eV] or less. This is because those peaks beyondthe above-mentioned range of the bond energy may not be photoelectronsemitted from the Si—N bond or the Si—O bonds.

The nitrogen-containing layer preferably has a ratio of 0.88 or morewhere the ratio is obtained by dividing the number of existing Si₃N₄bonds by the total number of the existing Si₃N₄ bonds, existingSi_(a)N_(b) bonds (where b/[a+b]<4/7), Si—Si bonds, Si—O bonds, andSi—ON bonds. The nitrogen-containing layer with a high abundance ratioof stable bonds is high in ArF lightfastness and chemical resistance.Among the above-mentioned bonds, the Si—O bonds are most stable.However, from the above-mentioned limitation, it is difficult to makethe nitrogen-containing layer contain a large amount of oxygen. Amongthe bonds of silicon and other elements except oxygen, Si₃N₄ bonds aremost stable. The above-mentioned nitrogen-containing layer having a highabundance ratio of the Si₃N₄ bonds is high in ArF lightfastness andchemical resistance.

The total film thickness of all of the nitrogen-containing layers in thephase shift film 2 is preferably 30 nm or more. If the total filmthickness of all of the nitrogen-containing layers is smaller than 30nm, a predetermined transmittance (40% or less) and a predeterminedphase difference (150 degrees or more and 200 degrees or less) requiredas the phase shift film may not be obtained. The total film thickness ofall of the nitrogen-containing layers is more preferably 35 nm or more,further preferably 40 nm or more. On the other hand, the total filmthickness of all of the nitrogen-containing layers in the phase shiftfilm 2 is preferably 60 nm or less, more preferably 55 nm or less.

The oxygen-containing layer is preferably formed of a materialconsisting of silicon and oxygen or a material consisting of oxygen,silicon, and one or more elements selected from metalloid elements andnon-metal elements. The oxygen-containing layer may contain anymetalloid elements. Among the metalloid elements, one or more elementsselected from boron, germanium, antimony, and tellurium are preferablycontained because an increase in conductivity of silicon used as asputtering target is expected.

The oxygen-containing layer may contain any non-metal elements. Thenon-metal elements in this case include narrow-sense non-metal elements(nitrogen, carbon, oxygen, phosphorus, sulfur, and selenium), halogens,and noble gases. Among the non-metal elements, one or more elementsselected from carbon, fluorine, and hydrogen are preferably contained.From the similar reason to that in case of the nitrogen-containinglayer, the oxygen-containing layer may contain a noble gas.

In the oxygen-containing layer, the total content of nitrogen and oxygenis preferably 50 atomic % or more. Taking into account increasing thedegree of freedom in designing the phase shift film 2 (in particular,transmittance), the total content of nitrogen and oxygen in theoxygen-containing layer is preferably 50 atomic % or more, morepreferably 55 atomic % or more, further preferably 60 atomic % or more.The total content of nitrogen and oxygen in the oxygen-containing layeris preferably 66 atomic % or less. If the oxygen-containing layercontains nitrogen and oxygen at a mixing ratio greater than that in SiO₂and Si₃N₄, it is difficult to form the oxygen-containing layer into anamorphous or a microcrystalline structure. In addition, surfaceroughness of the oxygen-containing layer is seriously degraded.

The oxygen-containing layer is preferably formed of a materialconsisting of silicon, nitrogen, and oxygen. In particular, in casewhere the degree of freedom in designing the phase shift film is widenedin a high-transmittance region, the oxygen-containing layer may beformed of a material consisting of silicon and oxygen. In this case, itmay be recognized that the material consisting of silicon, nitrogen, andoxygen or the material consisting of silicon and oxygen encompasses amaterial containing a noble gas.

The oxygen-containing layer preferably has an oxygen content of 15atomic % or more. In the silicon-based film, as the oxygen content isgreater, an extinction coefficient k is considerably decreased ascompared with the case where the nitrogen content is increased. In casewhere the degree of freedom in designing the phase shift film is widenedin the high-transmittance region, the oxygen content in theoxygen-containing layer is preferably 15 atomic % or more, morepreferably 20 atomic % or more, further preferably 25 atomic % or more.

The total film thickness of all of the oxygen-containing layers in thephase shift film 2 is preferably 10 nm or more, more preferably 15 nm ormore, further preferably 20 nm or more. On the other hand, the totalfilm thickness of all of the oxygen-containing layers in the phase shiftfilm 2 is preferably 50 nm or less, more preferably 45 nm or less.

The nitrogen-containing layer and the oxygen-containing layer mostpreferably have the amorphous structure because pattern edge roughnessis excellent when the pattern is formed by etching. In case where thenitrogen-containing layer or the oxygen-containing layer has acomposition difficult to form the amorphous structure, a state where theamorphous structure and the microcrystalline structure are mixed ispreferable.

The nitrogen-containing layer preferably has a refractive index n of 2.3or more, more preferably 2.4 or more. The nitrogen-containing layerpreferably has an extinction coefficient k of 0.5 or less, morepreferably 0.4 or less. On the other hand, the nitrogen-containing layerpreferably has a refractive index n of 3.0 or less, more preferably 2.8or less. The nitrogen-containing layer preferably has an extinctioncoefficient k of 0.16 or more, more preferably 0.2 or more.

The oxygen-containing layer preferably has a refractive index n of 1.5or more, more preferably 1.8 or more. The oxygen-containing layerpreferably has an extinction coefficient k of 0.15 or less, morepreferably 0.1 or less. On the other hand, the oxygen-containing layerpreferably has a refractive index n of 2.2 or less, more preferably 1.9or less. The oxygen-containing layer preferably has an extinctioncoefficient k of 0 or more.

A refractive index n and an extinction coefficient k of a thin film isnot determined only by a composition of the thin film. A film densityand a crystalline state of the thin film are also factors affecting therefractive index n and the extinction coefficient k. Therefore, byadjusting various conditions upon forming the thin film by reactivesputtering, the thin film is formed so that the thin film has a desiredrefractive index n and a desired extinction coefficient k. In order tomake each of the nitrogen-containing layer and the oxygen-containinglayer have the refractive index n and the extinction coefficient k indesired ranges, not only the ratio of a mixture of the noble gas and areactive gas is adjusted upon forming the thin film by reactivesputtering. There are a wide variety of conditions such as a pressure inthe film-forming chamber during formation of the thin film by reactivesputtering, an electric power applied to the target, and a positionalrelationship such as a distance between the target and the transparentsubstrate. These film-forming conditions are specific to a film-formingapparatus and are appropriately adjusted so that the thin film to beformed has the desired refractive index n and the desired extinctioncoefficient k.

The nitrogen-containing layer and the oxygen-containing layer are formedby sputtering. Any sputtering such as DC sputtering, RF sputtering, andion beam sputtering may be applicable. In case where a target low inconductivity (silicon target, silicon compound target containing no or asmall content of metalloid element, and so on) is used, it is preferableto apply the RF sputtering or the ion beam sputtering. Taking afilm-forming rate into consideration, it is more preferable to apply theRF sputtering.

If the phase shift film 2 has large film stress, there arises a problemthat, when the phase shift mask is manufactured from the mask blank,displacement of the transfer pattern formed on the phase shift film 2 isincreased. The film stress of the phase shift film 2 is preferably 275MPa or less, more preferably 165 MPa or less, further preferably 110 MPaor less. The phase shift film 2 formed by the above-mentioned sputteringhas relatively large film stress. Therefore, the phase shift film 2after it is formed by sputtering is preferably subjected to heatingtreatment or light irradiation treatment by a flash lamp or the like soas to reduce the film stress of the phase shift film 2.

The mask blank 100 preferably has the light shielding film 3 on thephase shift film 2. Generally, in a phase shift mask 200 (see FIG. 2F),an outer peripheral region outside an area where the transfer pattern isto be formed (transfer pattern forming area) is required to secure anoptical density (OD) of a predetermined value or more so that, whenexposure transfer is carried out onto a resist film on a semiconductorwafer by using an exposure apparatus, the resist film is not affected byexposure light transmitted through the outer peripheral region. Theouter peripheral region of the phase shift mask 200 is at least requiredto have an optical density greater than 2.0. As described above, thephase shift film 2 has a function of transmitting the exposure light ata predetermined transmittance and the above-mentioned optical density isdifficult to be secured only by the phase shift film 2. Therefore, in astage of manufacturing the mask blank 100, it is desired that the lightshielding film 3 is formed as a layer on the phase shift film 2 in orderto supplement the insufficient optical density. With the mask blank 100having the above-mentioned configuration, it is possible to manufacturethe phase shift mask 200 with the above-mentioned optical densitysecured in the outer peripheral region if the light shielding film 3 inan area where the phase shift effect is used (basically, the transferpattern forming area) is removed in the middle of manufacturing thephase shift mask 200. The mask blank 100 preferably has an opticaldensity of 2.5 or more in the layered structure of the phase shift film2 and the light shielding film 3, more preferably 2.8 or more. In orderto reduce the film thickness of the light shielding film 3, the opticaldensity in the layered structure of the phase shift film 2 and the lightshielding film 3 is preferably 4.0 or less.

For the light shielding film 3, both of a single-layer structure and alayered structure of two or more layers are applicable. The lightshielding film 3 of the single-layer structure and each layer of thelight shielding film 3 having the layered structure of two or morelayers may have a configuration that a composition is substantially samein a thickness direction of the film or the layer or a configurationwith composition gradient in the thickness direction of the layer.

For the light shielding film 3, a material having a sufficient etchingselectivity for the etching gas used upon forming the pattern on thephase shift film 2 must be applied in case where no other film isinterposed between the light shielding film and the phase shift film 2.In this case, the light shielding film 3 is preferably formed of amaterial containing chromium. The material which forms the lightshielding film 3 and which contains chromium may be chromium metal or amaterial containing chromium and one or more elements selected fromoxygen, nitrogen, carbon, boron, and fluorine.

Generally, a chromium-based material is etched by a mixture of achlorine-based gas and an oxygen gas. However, the chromium metal is notso high in etching rate for such etching gas. Taking into accountincreasing the etching rate for the etching gas which is the mixture ofthe chlorine-based gas and the oxygen gas, a material containingchromium and one or more elements selected from oxygen, nitrogen,carbon, boron, and fluorine is preferably used as the material formingthe light shielding film 3. The material which forms the light shieldingfilm 3 and which contains chromium may further contain one or moreelements selected from molybdenum and tin. By containing one or moreelements selected from molybdenum and tin in the material containingchromium, it is possible to increase the etching rate for the mixture ofthe chlorine-based gas and the oxygen gas.

On the other hand, in case where another film is interposed between thelight shielding film 3 and the phase shift film 2 in the mask blank 100,the above-mentioned another film (etching stopper and etching mask film)is formed of the above-mentioned material containing chromium whereasthe light shielding film 3 is formed of the material containing silicon.The material containing chromium is etched by the mixture of thechlorine-based gas and the oxygen gas whereas the resist film formed ofan organic material is easily etched by the mixture. The materialcontaining silicon is generally etched by a fluorine-based gas or achlorine-based gas. Basically, these etching gases do not contain oxygenand, accordingly, an amount of reduction of the resist film of theorganic material can be decreased as compared with the case whereetching is carried out using the mixture of the chlorine-based gas andthe oxygen gas. Therefore, the film thickness of the resist film can bereduced.

The material containing silicon and forming the light shielding film 3may contain a transition metal or may contain a metal element other thanthe transition metal. The reason is as follows. In case where the phaseshift mask 200 is manufactured from the mask blank 100, a pattern formedby the light shielding film 3 is basically a light shielding zonepattern in the outer peripheral region and is irradiated with the ArFexposure light in a less cumulative amount as compared with a transferpattern forming region. In addition, the light shielding film 3 rarelyremains in a fine pattern and any substantial problem is unlikely tooccur even if ArF lightfastness is low. When the light shielding film 3contains a transition metal, a light shielding performance isconsiderably improved as compared with the case where no transitionmetal is contained. It is therefore possible to reduce the thickness ofthe light shielding film. The transition metal contained in the lightshielding film 3 may be any one metal selected from molybdenum (Mo),tantalum (Ta), tungsten (W), titanium (Ti), chromium (Cr), hafnium (Hf),nickel (Ni), vanadium (V), zirconium (Zr), ruthenium (Ru), rhodium (Rh),niobium (Nb), and palladium (Pd) or a compound of these metals.

On the other hand, as the material containing silicon and forming thelight shielding film 3, a material consisting of silicon and nitrogen ora material containing one or more element selected from metalloidelements and non-metal elements in addition to the material consistingof silicon and nitrogen may be applied.

The above-mentioned mask blank 100 comprising the light shielding film 3formed as a layer on the phase shift film 2 preferably has a structurein which a hard mask film 4 formed of a material having an etchingselectivity for the etching gas used in etching the light shielding film3 is further formed as a layer on the light shielding film 3. Since thelight shielding film 3 requires a function of securing a predeterminedoptical density, there is a limit in reducing the thickness thereof. Itis sufficient that the hard mask film 4 has a film thickness allowingthe hard mask film to function as an etching mask until completion ofdry etching to form a pattern on the light shielding film 3 directlythereunder. Basically, no optical limitation is imposed on the hard maskfilm. Therefore, the thickness of the hard mask film 4 can beconsiderably reduced as compared with the thickness of the lightshielding film 3. It is sufficient that the resist film of the organicmaterial has a film thickness allowing the resist film to function as anetching mask until completion of dry etching to form a pattern on thehard mask film 4. Therefore, the thickness of the resist film canconsiderably be reduced than in the past.

In case where the light shielding film 3 is formed of the materialcontaining chromium, the hard mask film 4 is preferably formed of theabove-mentioned material containing silicon. The hard mask film 4 inthis case tends to be low in adhesion with the resist film of theorganic material. Therefore, it is preferable to perform HMDS(Hexamethyldisilazane) treatment on a surface of the hard mask film 4 soas to improve the adhesion of the surface. More preferably, the hardmask film 4 in this case is formed of SiO₂, SiN, SiON, or the like. As amaterial of the hard mask film 4 in case where the light shielding film3 is formed of the material containing chromium, a material containingtantalum is applicable in addition to the above-mentioned materials. Thematerial containing tantalum in this case may be tantalum metal or amaterial containing tantalum and one or more elements selected fromnitrogen, oxygen, boron, and carbon. For example, the material may beTa, TaN, TaON, TaBN, TaBON, TaCN, TaCON, TaBCN, or TaBOCN. On the otherhand, when the light shielding film 3 is formed of the materialcontaining silicon, the hard mask film 4 is preferably formed of theabove-mentioned material containing chromium.

In the mask blank 100, the resist film of the organic material ispreferably formed in contact with the surface of the hard mask film 4 toa film thickness of 100 nm or less. In case of a fine patterncorresponding to the DRAM of hp 32 nm generation, the transfer pattern(phase shift pattern) to be formed on the hard mask film 4 is sometimesprovided with SRAF (Sub-Resolution Assist Feature) having a line widthof 40 nm. Even in this event, however, a cross-section aspect ratio ofthe resist pattern can be lowered to 1:2.5. Therefore, it is possible toprevent the resist pattern from being collapsed or detached duringdevelopment or rinsing of the resist film. More preferably, the resistfilm has a film thickness of 80 nm or less.

In FIGS. 2A to 2F, a process of manufacturing the phase shift mask 200from the mask blank 100 according to the embodiment of this disclosureis illustrated in schematic sectional views.

The phase shift mask 200 according to this disclosure comprises thetransparent substrate 1 and the phase shift film 2 formed thereon andprovided with the transfer pattern (phase shift pattern 2 a). The phaseshift mask 200 is characterized in that the phase shift film 2 (phaseshift pattern 2 a) at least contains a nitrogen-containing layer and anoxygen-containing layer; that the oxygen-containing layer is formed of amaterial consisting of silicon and oxygen, or a material consisting ofoxygen, silicon, and one or more elements selected from metalloidelements and non-metal elements; that the nitrogen-containing layer isformed of a material consisting of silicon and nitrogen, or a materialconsisting of silicon, nitrogen, and one or more elements selected fromnon-metal elements and metalloid elements, and that, when thenitrogen-containing layer is subjected to the X-ray photoelectronspectroscopy to obtain the maximum peak PSi_f of photoelectron intensityof an Si2p narrow spectrum in the nitrogen-containing layer and thetransparent substrate 1 is subjected to the X-ray photoelectronspectroscopy to obtain the maximum peak PSi_s of photoelectron intensityof an Si2p narrow spectrum in the transparent substrate 1, a numericalvalue (PSi_f)/(PSi_s) is 1.09 or less where the numerical value isobtained by dividing the maximum peak PSi_f in the nitrogen containinglayer by the maximum peak PSi_s in the transparent substrate.

The phase shift mask 200 is similar in technical characteristics to themask blank 100. The matters regarding the transparent substrate 1, thephase shift film 2, and the light shielding film 3 (light shieldingpattern) in the phase shift mask 200 are similar to those in the maskblank 100. The phase shift mask 200 mentioned above is improved in ArFlightfastness of the entire phase shift film 2 (phase shift pattern 2 a)and also improved in chemical resistance. Therefore, when the phaseshift mask 200 is set on a mask stage of an exposure apparatus with anArF excimer laser used as exposure light and the phase shift pattern 2 ais exposure-transferred to a resist film on a semiconductor substrate,it is possible to transfer the pattern to the resist film on thesemiconductor substrate with an accuracy sufficiently satisfying adesign specification.

Hereinafter, according to a manufacturing process illustrated in FIGS.2A to 2F, one example of a method for manufacturing the phase shift mask200 will be described. In this example, the material containing chromiumis used as the light shielding film 3 whereas the material containingsilicon is used as the hard mask film 4.

At first, the resist film was formed by spin coating in contact with thehard mask film 4 in the mask blank 100. Next, on the resist film, afirst pattern as a transfer pattern (phase shift pattern) to be formedon the phase shift film 2 was written by exposure. Furthermore, apredetermined process such as development was carried out to form afirst resist pattern 5 a having the phase shift pattern (see FIG. 2A).Subsequently, with the first resist pattern 5 a used as a mask, dryetching using a fluorine-based gas was carried out to form a firstpattern (hard mask pattern 4 a) on the hard mask film 4 (see FIG. 2B).

Next, after removing the resist pattern 5 a, dry etching using a mixtureof a chlorine-based gas and an oxygen gas was carried out with the hardmask pattern 4 a used as a mask, to form a first pattern (lightshielding pattern 3 a) on the light shielding film 3 (see FIG. 2C).Subsequently, with the light shielding pattern 3 a used as a mask, dryetching using a fluorine-based gas was carried out to form the firstpattern (phase shift pattern 2 a) on the phase shift film 2 andsimultaneously remove the hard mask pattern 4 a (see FIG. 2D).

Next, the resist film was formed on the mask blank 100 by spin coating.Next, a second pattern as a pattern to be formed on the light shieldingfilm 3 (light shielding pattern) was written by exposure on the resistfilm. Furthermore, a predetermined process such as development wascarried out to form a second resist pattern 6 b having the lightshielding pattern. Subsequently, with the second resist pattern 6 b usedas a mask, dry etching using a mixture of a chlorine-based gas and anoxygen gas was carried out to form the second pattern (light shieldingpattern 3 b) on the light shielding film 3 (see FIG. 2E). Furthermore,the second resist pattern 6 b was removed. Through a predeterminedprocess such as cleaning, the phase shift mask 200 was obtained (seeFIG. 2F).

The chlorine-based gas used in the dry etching mentioned above is notparticularly limited as far as Cl is contained. For example, thechlorine-based gas may be Cl₂, SiCl₂, CHCl₃, CH₂Cl₂, CCl₄, BCl₃, and soon. The fluorine-based gas used in the dry etching mentioned above isnot particularly limited as far as F is contained. For example, thefluorine-based gas may be CHF₃, CF₄, C₂F₆, C₄F₈, SF₆, and so on. Inparticular, since the fluorine-based gas free from C is relatively lowin etching rate for the transparent substrate 1 of a glass material, adamage against the transparent substrate 1 can further be reduced.

Furthermore, a method for manufacturing a semiconductor device accordingto this disclosure is characterized in that the pattern isexposure-transferred to the resist film on the semiconductor substrateusing the phase shift mask 200 manufactured using the mask blank 100mentioned above. The mask blank 100 according to this disclosure and thephase shift mask 200 manufactured using the mask blank 100 have theeffect as mentioned above. Therefore, when the phase shift mask 200 isset on the mask stage of the exposure apparatus with the ArF excimerlaser used as the exposure light and the phase shift pattern 2 a isexposure-transferred to the resist film on the semiconductor substrate,it is possible to transfer the pattern onto the resist film on thesemiconductor substrate with an accuracy sufficiently satisfying thedesign specification.

On the other hand, as another embodiment related to this disclosure, amask blank having the following configuration is given. Specifically,the mask blank according to another embodiment comprises a transparentsubstrate and a phase shift film formed thereon and is characterized inthat the phase shift film is a single-layer film having a compositiongradient portion which is formed on its surface on the side oppositefrom the transparent substrate and in a region adjacent thereto andwhich is increased in oxygen content; that the phase shift film isformed of a material consisting of silicon and nitrogen, or a materialconsisting of nitrogen, silicon, and one or more elements selected fromnon-metal elements and metalloid elements; and that, when the phaseshift film is subjected to the X-ray photoelectron spectroscopy toobtain the maximum peak PSi_f of photoelectron intensity of an Si2pnarrow spectrum in the phase shift film and the transparent substrate issubjected to the X-ray photoelectron spectroscopy to obtain the maximumpeak PSi_s of photoelectron intensity of an Si2p narrow spectrum in thetransparent substrate, a numerical value (PSi_f)/(PSi_s) is 1.09 or lesswhere the numerical value is obtained by dividing the maximum peak PSi_fin the phase shift film by the maximum peak PSi_s in the transparentsubstrate.

A region of the phase shift film except the composition gradient portionhas characteristics similar to those of the nitrogen-containing layer ofthe phase shift mask according to this disclosure. The compositiongradient portion of the phase shift film is high in both ArFlightfastness and chemical resistance because the oxygen content islarge. Therefore, as compared with an existing mask blank having asingle-layer structure and formed of a silicon nitride-based material,the mask blank according to another embodiment is high in ArFlightfastness of the entire phase shift film and also in chemicalresistance. Other matters regarding the phase shift film of anotherembodiment are similar to those of the nitrogen-containing layer in thephase shift film according to the embodiment of this disclosure.

Furthermore, a phase shift mask according to another embodiment, similarin characteristics to the mask blank of another embodiment mentionedabove, may be given. Specifically, the phase shift mask according toanother embodiment comprises a transparent substrate and a phase shiftfilm formed thereon and provided with a transfer pattern and ischaracterized in that the phase shift film is a single-layer film havinga composition gradient portion which is formed on its surface on theside opposite from the transparent substrate and in a region adjacentthereto and which is increased in oxygen content; that the phase shiftfilm is formed of a material consisting of silicon and nitrogen or amaterial consisting of nitrogen, silicon, and one or more elementsselected from non-metal elements and metalloid elements, and that, whenthe phase shift film is subjected to the X-ray photoelectronspectroscopy to obtain the maximum peak PSi_f of photoelectron intensityof an Si2p narrow spectrum in the phase shift film and the transparentsubstrate is subjected to the X-ray photoelectron spectroscopy to obtainthe maximum peak PSi_s of photoelectron intensity of an Si2p narrowspectrum in the transparent substrate, a numerical value (PSi_f)/(PSi_s)is 1.09 or less where the numerical value is obtained by dividing themaximum peak PSi_f in the phase shift film by the maximum peak PSi_s inthe transparent substrate.

Like in case of the mask blank according to another embodiment mentionedabove, the phase shift mask of another embodiment is high in ArFlightfastness of the entire phase shift film and in chemical resistanceas compared with an existing phase shift mask comprising a phase shiftfilm having a single layer structure and formed of a siliconnitride-based material. When the phase shift mask of this embodiment isset on the mask stage of the exposure apparatus with the ArF excimerlaser used as the exposure light and the phase shift pattern isexposure-transferred to the resist film on the semiconductor substrate,it is possible to transfer the pattern to the resist film on thesemiconductor substrate with an accuracy sufficiently satisfying thedesign specification.

EXAMPLES

Hereinafter, the embodiments of this disclosure will more specificallybe described with reference to examples.

Example 1

[Manufacture of Mask Blank]

A transparent substrate 1 made of synthetic quartz glass with a mainsurface having a size of about 152 mm×about 152 mm and a thickness ofabout 6.25 mm was prepared. In the transparent substrate 1, an end faceand the main surface were polished to a predetermined surface roughness.Thereafter, the transparent substrate was subjected to predeterminedcleaning and predetermined drying.

Next, on the transparent substrate 1, a phase shift film 2 having atwo-layer structure comprising a nitrogen-containing layer and anoxygen-containing layer was formed through the following steps. Atfirst, the transparent substrate 1 was placed in a single-wafer DCsputtering apparatus and, using a silicon (Si) target and a mixture ofkrypton (Kr), helium (He), and nitrogen (N₂) as a sputtering gas,reactive sputtering (RF sputtering) by an RF power supply was carriedout to form, on the transparent substrate 1, the nitrogen-containinglayer (silicon nitride layer), consisting of silicon and nitrogen, ofthe phase shift film 2 to a thickness of 58 nm.

Next, the transparent substrate 1 provided with the nitrogen-containinglayer was placed in the single-wafer DC sputtering apparatus. Using asilicon dioxide (SiO₂) target and an argon (Ar) gas as a sputtering gas,reactive sputtering (RF sputtering) by the RF power supply was carriedout to form, on the nitrogen-containing layer, an oxygen-containinglayer (silicon oxide layer), consisting of silicon and oxygen, of thephase shift film 2 to a thickness of 11 nm.

Next, the transparent substrate 1 provided with the phase shift film 2was placed in an electric furnace and subjected to heat treatment in airunder conditions of a heating temperature of 550° C. and a treatmenttime of 1 hour. The electric furnace similar in structure to a verticalfurnace disclosed in FIG. 5 of JP 2002-162726 A was used. The heattreatment in the electric furnace was carried out in a state where airpassing through a chemical filter was introduced into the furnace. Afterthe heat treatment in the electric furnace, a refrigerant was introducedinto the electric furnace to carry out forced cooling on the substrateto a predetermined temperature (around 250° C.). The forced cooling wasperformed in a state where a nitrogen gas as the refrigerant wasintroduced into the furnace (substantially in a nitrogen gasatmosphere). After the forced cooling, the substrate was taken out fromthe electric furnace and subjected to natural cooling in air down tonormal temperature (25° C. or lower)

For the phase shift film 2 after the heat treatment, a transmittance anda phase difference at a wavelength (about 193 nm) of the ArF excimerlaser light were measured by a phase shift measurement apparatus(MPM-193 manufactured by Lasertec Corporation). As a result, thetransmittance was 21% and the phase difference was 177 degrees.

On a main surface of a transparent substrate newly prepared, a phaseshift film was formed in the same conditions as the phase shift filmmentioned above. Furthermore, heat treatment was carried out in the sameconditions as mentioned above. Thereafter, optical characteristics ofthe phase shift film were measured using a spectroscopic ellipsometer(M-2000D manufactured by J. A. Woollam Co.). As a result, thenitrogen-containing layer had a refractive index n of 2.56 and anextinction coefficient k of 0.35 at the wavelength of 193 nm whereas theoxygen-containing layer had a refractive index n of 1.59 and anextinction coefficient of 0.00 at the wavelength of 193 nm.

Next, on a main surface of a transparent substrate newly prepared inaddition to that mentioned above, a phase shift film was formed in thesame film-forming conditions as the phase shift film 2 in Example 1.Furthermore, heat treatment was carried out in the same conditions asmentioned above. Then, the transparent substrate and the phase shiftfilm after the heat treatment were subjected to the X-ray photoelectronspectroscopy. In the X-ray photoelectron spectroscopy, a surface of thephase shift film (or the transparent substrate) was irradiated with theX-rays (AlKα rays: 1486 eV) and the intensity of photoelectrons emittedfrom the phase shift film (or the transparent substrate) was measured.The surface of the phase shift film (or the transparent substrate) waseroded by Ar gas sputtering for a predetermined time (the depth of about0.7 nm). The phase shift film (or the transparent substrate) in aneroded region was irradiated with the X-rays and the intensity ofphotoelectrons emitted from the phase shift film (or the transparentsubstrate) in the eroded region was measured. By repeating theabove-mentioned step, the Si2p narrow spectrum was acquired for each ofthe phase shift film and the transparent substrate. In the Si2p narrowspectrum thus acquired, because the transparent substrate 1 is aninsulator, an energy is displaced downward as compared with a spectrumin case of analysis performed on a conductor. In order to correct thedisplacement, correction is performed in conformity with a peak ofcarbon as a conductor. The X-ray photoelectron spectroscopy was carriedout using AlKα rays (1486.6 eV) as the X-rays under the conditions thata photoelectron detection region was a circular area with a diameter of200 μm and a takeoff angle was 45 deg (same in the following comparativeexample).

In FIG. 3, the Si2P narrow spectrum of each of the nitrogen-containinglayer (silicon nitride layer) of the phase shift film and thetransparent substrate in Example 1 is illustrated. From the result ofthe X-ray photoelectron spectroscopy, a value (PSi_f)/(PSi_s) obtainedby dividing the maximum peak PSi_f of the Si2p narrow spectrum in thenitrogen-containing layer of the phase shift film by the maximum peakPSi_s of the Si2p narrow spectrum in the transparent substrate wascalculated to be equal to 1.077.

The obtained Si2p narrow spectrum of the nitrogen-containing layerincludes peaks of Si₃N₄ bonds, Si_(a)N_(b) bonds (b/[a+b]<4/7), Si—Obonds, and SiON bonds. Fixing a peak position and a full width at halfmaximum FWHM for each of Si₃N₄ bonds, Si_(a)N_(b) bonds, Si—O bonds, andSiON bonds (where Si—O bonds and Si—ON bonds have the same peakposition), peak resolution was carried out. Specifically, with the peakposition of Si_(a)N_(b) bonds fixed at 100.4 eV, the peak position ofSi₃N₄ fixed at 102.0 eV, the peak position of each of Si—O bonds andSi—ON bonds fixed at 103.3 eV, and the full width at half maximum FWHMof those bonds fixed at 2.06, peak resolution was carried out (same inthe following Comparative Example 1).

Furthermore, for the spectrum of each of Si_(a)N_(b) bonds, Si₃N₄ bonds,Si—O bonds, and SiON bonds after peak resolution, an area obtained bysubtracting a background calculated by an algorithm of a known techniqueequipped in an analyzing apparatus was calculated. Based on each areathus calculated, the proportion of existing Si_(a)N_(b) bonds, theproportion of existing Si₃N₄ bonds, and the proportion of existing Si—Obonds and existing Si—ON bonds were calculated. As a result, theproportion of the existing Si_(a)N_(b) bonds was 0.092, the proportionof the existing Si₃N₄ bonds was 0.884, and the proportion of theexisting Si—O bonds and the existing Si—ON bonds was 0.024. Thus, thenitrogen-containing layer satisfies the condition that the ratioobtained by dividing the number of the existing Si₃N₄ bonds by the totalnumber of the existing Si₃N₄ bonds, the existing Si_(a)N_(b) bonds, theexisting Si—O bonds, and the existing Si—ON bonds was 0.88 or more(0.884, satisfactory). From the result of the X-ray photoelectronspectroscopy, it has been found out that the nitrogen-containing layerof the phase shift film had a composition of Si:N:O=43.6 atomic %:55.2atomic %:1.2 atomic % and that the oxygen-containing layer had acomposition of Si:O=33.8 atomic %:66.2 atomic %.

Next, the transparent substrate 1 provided with the phase shift film 2after heat treatment was placed in the single-wafer DC sputteringapparatus. Using a chromium (Cr) target and a mixture of argon (Ar),carbon dioxide (CO₂), and helium (flow rate ratio Ar:CO₂:He=18:33:28,pressure=0.15 Pa) as a sputtering gas with an electric power of 1.8 kWfrom a DC power supply, reactive sputtering (DC sputtering) was carriedout to form the light shielding film 3 of CrOC to a thickness of 56 nmin contact with the phase shift film 2.

Furthermore, the transparent substrate 1 with the phase shift film 2 andthe light shielding film 3 formed as layers was placed in thesingle-wafer RF sputtering apparatus. Using a silicon dioxide (SiO₂)target and an argon (Ar) gas (pressure=0.03 Pa) as a sputtering gas withan electric power of 1.5 kW from the DC power supply, RF sputtering wascarried out to form the hard mask film 4 consisting of silicon andoxygen on the light shielding film 3 to a thickness of 5 nm. By theabove-mentioned steps, the mask blank 100 having a structure in whichthe phase shift film 2, the light shielding film 3, and the hard maskfilm 4 are formed as layers on the transparent substrate 1 wasmanufactured.

[Manufacture of Phase Shift Mask]

Next, using the mask blank 100 of Example 1, the phase shift mask 200 ofExample 1 was manufactured through the following steps. At first, asurface of the hard mask film 4 was subjected to HMDS treatment.Subsequently, a resist film of a chemically amplified resist forelectron beam writing was formed by spin coating in contact with thesurface of the hard mask film 4 to a film thickness of 80 nm. Then, onthe resist film, a first pattern as a phase shift pattern to be formedon the phase shift film 2 was formed by electron beam writing.Predetermined development and predetermined cleaning were carried out toform a first resist pattern 5 a having the first pattern (see FIG. 2A).

Next, using the first resist pattern 5 a as a mask, dry etching using aCF₄ gas was carried out to form the first pattern (hard mask pattern 4a) on the hard mask film 4 (see FIG. 2B).

Then, the first resist pattern 5 a was removed. Subsequently, using thehard mask pattern 4 a as a mask and a mixture of chlorine and oxygen(gas flow rate ratio Cl₂:O₂=4:1), dry etching was carried out to formthe first pattern (light shielding pattern 3 a) on the light shieldingfilm 3 (see FIG. 2C).

Next, with the light shielding pattern 3 a used as a mask and using afluorine-based gas (mixture of SF₆ and He), dry etching was carried outto form the first pattern (phase shift pattern 2 a) on the phase shiftfilm 2 and to remove the hard mask pattern 4 a simultaneously (see FIG.2D).

Next, on the light shielding pattern 3 a, a resist film of a chemicallyamplified resist for electron beam writing was formed by spin coating toa film thickness of 150 nm. Then, on the resist film, a second patternas a pattern (light shielding pattern) to be formed on the lightshielding film 3 was written by exposure. Furthermore, a predeterminedprocess such as development was carried out to form a second resistpattern 6 b having the light shielding pattern. Subsequently, with thesecond resist pattern 6 b used as a mask and using a mixture of chlorineand oxygen (gas flow rate ratio Cl₂:O₂=4:1), dry etching was carried outto form the second pattern (light shielding pattern 3 b) on the lightshielding film 3 (see FIG. 2E). Furthermore, the second resist pattern 6b was removed and, through cleaning, the phase shift mask 200 wasobtained (see FIG. 2F).

The phase shift pattern 2 a of the halftone phase shift mask 200 inExample 1 thus manufactured was subjected to intermittent irradiationwith the ArF excimer laser light in a cumulative irradiation amount of40 kJ/cm². CD (Critical Dimension) variation of the phase shift pattern2 a before and after the irradiation was 1.2 nm at maximum, which is theCD variation capable of assuring high transfer accuracy as the phaseshift mask 200.

Through the similar steps, the halftone phase shift mask 200 in Example1 was additionally manufactured. The phase shift mask 200 was subjectedto cleaning by a chemical solution. Specifically, the phase shift mask200 was repeatedly subjected to 20 cycles of cleaning step where onecycle includes SPM cleaning (cleaning liquid: H₂SO₄+H₂O₂) at first,rinse cleaning with DI (DeIonized) water next, APM cleaning (cleaningliquid: NH₄OH+H₂O₂+H₂O) next, and rinse cleaning with DI water last. Thephase shift pattern 2 a of the phase shift mask 200 after the cleaningwas observed by a cross-sectional TEM (Transmission ElectronMicroscope). As a result, it has been confirmed that the phase shiftpattern 2 a had an excellent side wall shape. No remarkable unevennesswas found between the silicon nitride layer and the silicon oxide layer.

Next, by using AIMS193 (manufactured by Carl Zeiss AG), the phase shiftmask 200 of Example 1 after the cumulative irradiation with the ArFexcimer laser light was subjected to simulation of a transfer image whenexposure transfer onto the resist film on the semiconductor substratewas carried out with exposure light having a wavelength of 193 nm.Examining an exposure transfer image in the simulation, the designspecification was fully satisfied. From this result, it is said that acircuit pattern can finally be formed on the semiconductor substratewith high accuracy when the phase shift mask 200 in Example 1 after thecumulative irradiation with the ArF excimer laser light is set on themask stage of the exposure apparatus and exposure transfer is carriedout onto the resist film on the semiconductor substrate.

Comparative Example 1

[Manufacture of Mask Blank]

A mask blank in Comparative Example 1 was manufactured through the stepssimilar to those for the mask blank 100 in Example 1 except thatconditions of heat treatment on a phase shift film were changed.Specifically, a transparent substrate 1 provided with a phase shift film2 in Comparative Example 1 was placed on a hot plate and subjected toheat treatment in air under conditions of a heating temperature of 280°C. and a treatment time of 30 minutes. After the heat treatment, forcedcooling was carried out down to normal temperature (25° C. or lower) byusing a refrigerant.

For the phase shift film after the heat treatment, a transmittance and aphase difference at a wavelength (about 193 nm) of ArF excimer laserlight were measured by a phase shift measurement apparatus (MPM-193manufactured by Lasertec Corporation). As a result, the transmittancewas 21% and the phase difference was 177 degrees. In the manner similarto the case in Example 1, optical characteristics of the phase shiftfilm were measured. As a result, a nitrogen-containing layer had arefractive index n of 2.58 and an extinction coefficient k of 0.39 atthe wavelength of 193 nm whereas an oxygen-containing layer had arefractive index n of 1.59 and an extinction coefficient of 0.00 at thewavelength of 193 nm.

In the manner similar to Example 1, on a main surface of a transparentsubstrate newly prepared, a phase shift film was formed in the samefilm-forming conditions as the phase shift film in ComparativeExample 1. Furthermore, heat treatment was carried out in the sameconditions. Next, the transparent substrate and the phase shift filmafter the heat treatment were subjected to the X-ray photoelectronspectroscopy similar to that in Example 1.

FIG. 4 shows an Si2p narrow spectrum of each of the nitrogen-containinglayer (silicon nitride layer) of the phase shift film and thetransparent substrate in Comparative Example 1. From the result of theX-ray photoelectron spectroscopy, a value (PSi_f)/(PSi_s) obtained bydividing the maximum peak PSi_f of the Si2p narrow spectrum in thenitrogen-containing layer of the phase shift film by the maximum peakPSi_s of the Si2p narrow spectrum in the transparent substrate wascalculated. As a result, the value was equal to 1.096.

In the manner similar to Example 1, the Si2p narrow spectrum of thenitrogen containing layer in Comparative Example 1 was subjected to peakresolution of Si₃N₄ bonds, Si_(a)N_(b) bonds (b/[a+b]<4/7), Si—O bonds,and SiON bonds and the proportion of existing bonds was calculated foreach. As a result, the proportion of existing Si_(a)N_(b) bonds was0.093, the proportion of existing Si₃N₄ bonds was 0.873, and theproportion of existing Si—O bonds and existing Si—ON bonds was 0.034.Thus, the nitrogen-containing layer in Comparative Example 1 does notsatisfy the condition that the ratio obtained by dividing the number ofthe existing Si₃N₄ bonds by the total number of the existing Si₃N₄bonds, the existing Si_(a)N_(b) bonds, the existing Si—O bonds, and theexisting Si—ON bonds was 0.88 or more (0.873, not satisfactory). Fromthe result of the X-ray photoelectron spectroscopy, it has been foundout that the nitrogen-containing layer of the phase shift film inComparative Example 1 had a composition of Si:N:O=43.8 atomic %:54.5atomic %:1.7 atomic % and that the oxygen-containing layer had acomposition of Si:O=33.9 atomic %:66.1 atomic %.

Next, in the manner similar to Example 1, a light shielding film and ahard mask film were formed on the phase shift film of the transparentsubstrate. By the above-mentioned steps, the mask blank in ComparativeExample 1 having a structure in which the phase shift film, the lightshielding film, and the hard mask film are formed as layers on thetransparent substrate was manufactured.

[Manufacture of Phase Shift Mask]

Next, using the mask blank in Comparative Example 1, a phase shift maskin Comparative Example 1 was manufactured through the steps similar tothose in Example 1. Furthermore, in the manner similar to Example 1, aphase shift pattern of the manufactured halftone phase shift mask inComparative Example 1 was subjected to intermittent irradiation with theArF excimer laser light in a cumulative irradiation amount of 40 kJ/cm².CD (Critical Dimension) variation of the phase shift pattern before andafter the irradiation was 3.5 nm at maximum. Thus, the CD variationcapable of assuring high transfer accuracy as the phase shift mask wasnot reached.

Next, using the mask blank in Comparative Example 1 and through thesteps similar to those in Example 1, a halftone phase shift mask inComparative Example 1 was additionally manufactured. The phase shiftmask was subjected to cleaning by chemical solution. A phase shiftpattern of the phase shift mask after the cleaning was observed bycross-sectional TEM (Transmission Electron Microscope). As a result, ithas been confirmed that the phase shift pattern had a side wall shapewith an unevenness between the silicon nitride layer and the siliconoxide layer.

Next, the phase shift mask in Comparative Example 1 after the cumulativeirradiation with the ArF excimer laser light is subjected to simulationof a transfer image when exposure transfer onto the resist film on thesemiconductor substrate was carried out with exposure light having awavelength of 193 nm by using AIMS193 (manufactured by Carl Zeiss AG).Examining an exposure transfer image in the simulation, the designspecification was not satisfied in an area of a fine pattern. From thisresult, it is difficult to finally form a circuit pattern on thesemiconductor substrate with high accuracy when the phase shift mask inComparative Example 1 after the cumulative irradiation with the ArFexcimer laser light is set on the mask stage of the exposure apparatusand exposure transfer is carried out onto the resist film on thesemiconductor substrate.

EXPLANATION OF REFERENCE NUMERALS

-   -   1 transparent substrate    -   2 phase shift film    -   2 a phase shift pattern    -   3 light shielding film    -   3 a, 3 b light shielding pattern    -   4 hard mask film    -   4 a hard mask pattern    -   5 a first resist pattern    -   6 b second resist pattern    -   100 mask blank    -   200 phase shift mask

The invention claimed is:
 1. A mask blank comprising: a transparentsubstrate; and a phase shift film containing silicon and nitrogen, andformed on the transparent substrate, wherein the phase shift film is asingle-layer film having a composition gradient portion, wherein thecomposition gradient portion is formed on a surface of the phase shiftfilm on the side opposite from the transparent substrate and in a regionadjacent to the surface, wherein the composition gradient portion isincreased in oxygen content, wherein, when the phase shift film issubjected to X-ray photoelectron spectroscopy to obtain a maximum peakPSi_f of photoelectron intensity of an Si2p narrow spectrum in the phaseshift film and the transparent substrate is subjected to X-rayphotoelectron spectroscopy to obtain a maximum peak PSi_s ofphotoelectron intensity of an Si2p narrow spectrum in the transparentsubstrate, a numerical value (PSi_f)/(PSi_s) is 1.09 or less where thenumerical value is obtained by dividing the maximum peak PSi_f in thephase shift film by the maximum peak PSi_s in the transparent substrate.2. The mask blank according to claim 1, wherein a region of the phaseshift film other than the composition gradient portion has a nitrogencontent of 50 atomic % or more.
 3. The mask blank according to claim 1,wherein a region of the phase shift film other than the compositiongradient portion has a silicon content of 35 atomic % or more.
 4. Themask blank according to claim 1, wherein a region of the phase shiftfilm other than the composition gradient portion has an oxygen contentof 10 atomic % or less.
 5. The mask blank according to claim 1, whereinthe maximum peak of photoelectron intensity in the Si2p narrow spectrumis the maximum peak at a bond energy within a range of 96 [eV] or moreand 106 [eV] or less.
 6. The mask blank according to claim 1, whereinthe X-ray photoelectron spectroscopy to which the phase shift film issubjected is carried out using AlKα X-rays.
 7. The mask blank accordingto claim 1, wherein a ratio of the proportion of Si₃N₄ bonds that existin an area of the phase shift film other than the composition gradientportion to a total proportion of Si₃N₄ bonds, Si_(a)N_(b) bonds (whereb/[a+b]<4/7), Si—O bonds, and Si—ON bonds that exist in the area of thephase shift film other than the composition gradient portion is 0.88 ormore.
 8. The mask blank according to claim 1, wherein a transmittance ofthe phase shift film with respect to exposure light of an ArF excimerlaser is 10% or more; and the phase shift film is configured to transmitthe exposure light so that transmitted light has a phase difference of150 degrees or more and 200 degrees or less with respect to the exposurelight transmitted through air for a same distance as a thickness of thephase shift film.
 9. The mask blank according to claim 1, comprising alight shielding film formed on the phase shift film.
 10. A phase shiftmask comprising: a transparent substrate; and a phase shift film with atransfer pattern containing silicon and nitrogen, and formed on thetransparent substrate, wherein the phase shift film is a single-layerfilm having a composition gradient portion, wherein the compositiongradient portion is formed on a surface of the phase shift film on theside opposite from the transparent substrate and in a region adjacent tothe surface, wherein the composition gradient portion is increased inoxygen content, wherein, when the phase shift film is subjected to X-rayphotoelectron spectroscopy to obtain a maximum peak PSi_f ofphotoelectron intensity of an Si2p narrow spectrum in the phase shiftfilm and the transparent substrate is subjected to X-ray photoelectronspectroscopy to obtain a maximum peak PSi_s of photoelectron intensityof an Si2p narrow spectrum in the transparent substrate, a numericalvalue (PSi_f)/(PSi_s) is 1.09 or less where the numerical value isobtained by dividing the maximum peak PSi_f in the phase shift film bythe maximum peak PSi_s in the transparent substrate.
 11. The phase shiftmask according to claim 10, wherein the phase shift film other than thecomposition gradient portion has a nitrogen content of 50 atomic % ormore.
 12. The phase shift mask according to claim 10, wherein the phaseshift film other than the composition gradient portion has a siliconcontent of 35 atomic % or more.
 13. The phase shift mask according toclaim 10, wherein the phase shift film other than the compositiongradient portion has an oxygen content of 10 atomic % or less.
 14. Thephase shift mask according to claim 10, wherein the maximum peak ofphotoelectron intensity in the Si2p narrow spectrum is the maximum peakat a bond energy within a range of 96 [eV] or more and 106 [eV] or less.15. The phase shift mask according to claim 10, wherein the X-rayphotoelectron spectroscopy to which the phase shift film is subjected iscarried out using AlKα X-rays.
 16. The phase shift mask according toclaim 10, wherein a ratio of the proportion of Si₃N₄ bonds that exist inan area of the phase shift film other than the composition gradientportion to a total proportion of Si₃N₄ bonds, Si_(a)N_(b) bonds (whereb/[a+b]<4/7), Si—O bonds, and Si—ON bonds that exist in the area of thephase shift film other than the composition gradient portion is 0.88 ormore.
 17. The phase shift mask according to claim 10, wherein atransmittance of the phase shift film with respect to exposure light ofan ArF excimer laser is 10% or more; and the phase shift film isconfigured to transmit the exposure light so that transmitted light hasa phase difference of 150 degrees or more and 200 degrees or less withrespect to the exposure light transmitted through air for a samedistance as a thickness of the phase shift film.
 18. The phase shiftmask according to claim 10, comprising a light shielding film formed onthe phase shift film and provided with a light shielding pattern.
 19. Amethod of manufacturing a semiconductor device, comprising using thephase shift mask according to claim 10 to exposure-transfer a transferpattern to a resist film on a semiconductor substrate.